Translucent paper base



April 21, 1953 M. SAL@ E'TAL 2,635,970

TRANSLUCENT PAPER BASE Filed Nov. 26. 1948 CELLULOSE ACEZITE BUTYAATECOAT/N5 0F D/Bl/TYL SEBACATE Bun/1. .STEM/:TE

(PAPE/e /Mmfsmrfo wmf Bury/MT5 CHLORl/VATE D D/PHE/VYL Mal-fin SaloHaroldlf? Vivian INVENTORS ATTORNEYS' The impregnating compositionshould contain a resin which imparts adhesiveness to the composition butis yet stable insofar that the resin is compatible with the otheringredients of the composition and is not guilty of blocking whenapplied as a melt coat. We have found that with cellulose acetatebutyrate the chlorinated diphenyls having a chlorine content more than40% are especially useful as the resin constituent. The cellulose esteremployed must be a butyric acid ester of cellulose having a butyrylcontent of at least 42%.

The plasticizer employed in the impregnating" composition should be asolvent-type plasticizer, such as dioctyl phthalate, dicapryl phthalate,di

4 the paper is preheated to 30G-330 F. and an overcoating composition ata temperature of 340- 360 F. is applied thereto. Any of the melt-coatingcompositions referred to in my patents listed above or in British PatentNo. 540,765, are useful in this operation, particularly to obtain acoating characterized by good iiexibility. The clearance on the rollsemployed in the coating operation should be such as to give a coat of.0003 to .0005 inch thickness on each side of the paper sheet. Thisaggregates 3 pounds of coating per side or 6 .pounds of coating for bothsides per 1000 square feet of paper surface. The product which isobtained readily transmits a large proportion butyl sebacate,di-ethyl-hexyl adipate, methoxyethyl phthalate, ethoxyethyl phthalate,and the like. These plasticizers can be mixed to a small' extent withother types of plasticizers providing the resulting material remains ofthe solvent type o r, in other wo-rds, will dissolve the cellulose esterat a temperature of 170-l80 C. The impregnating composition in additionto having a viscosity below 5000 centipoises at 170 C. must also be amaterial which exhibits a refractive index close to that of the paperwhich is treated.

vThe overcoatingcomposition which is applied as the second coat may beany melt-coating composition, such asv described in patents relatingthereto. This composition should vbe one which has a blocking p oint atabout 200 F. and forms a coating which has satisfactory flexibility. Acomposition of 75 parts of a cellulose acetate butyratefhaving a butyrylcontent of 45%, 15 parts of dibutyl sebacate, and 10 parts stearate isuseful for this purpose. Various melt-coating compositions which areeminently suitable for this overcoating have been described, such as inSalo Patents Nos. 2,387,773 and 2,387,774. Salo Patent No. 2,439,103 andMeyer Patent No. 2,439,- 093 also` discloses melt-coating compositionsuseful as the overcoating referred to. Any of these compositions wouldbe useful for the molten overcoating in preparingtranslucent paper baseas. described herein. Other melt-coating compositionswhich are usefulfor overcoating purposes inaccordance with out invention are describedin British Patent 100,540.7 65, dated October 29, 1941. The paper in'accordance with our invention may be, readily prepared by preheatingthe paper sheet to a Atemperature of G-250 F. and then applyingf theretoin a `melt-coating operation, such as described in British Patent No.540,765, a melt ofthe impregnating composition held at a temperature of30D-330 F. The paper is then subjected to pressure, such as bycalendering rolls having a temperature of 30G-360 F. at a pressureexceeding 500 p. s. i. and preferably 3000 to v5000 p. s. i. A usefulcomposition in this connection is made up of 50-70% of a chlorinateddiaryl, .particularly chlorinated diphenyl, having a chlorine content ofat least 40%, 20-30% of a cellulose acetate butyrate having a lowviscosity and a butyryl content of at least 45% and 5-15% of asolvent-type plasticizer. Compositions of this nature vare described adclaimed in U. S. Patent No. 2,481,637. Any of the compositions therein4which have a chlorinated diphenyl or Aoroclor lcontent of at least 50%and a melting point of less thanv 200 C. would be useful for thisimpregnating operation.

After the impregnated paper has been obtained and the impregnatingcomposition is set, the paper is then given an overcoating by passingthe paper through a melt-coating machine in which paper that subbingfirst be applied. One type of subbing which has been found to be usefulin this connection is formed by first applying a very thinlayer of acellulose nitrate of quitelow viscosity to thev melt coating, followedby a very thin layer of gelatin -applied thereto. The technique ofsubbing in this manner is described in U. S. Patent No. 2,014,547 ofBabcock, granted September 17, 1935. The disclosure of that patent maybe referred to as a guide for this type of subbing operation. Ifdesired, instead of vusing two layers, the nitrate and gelatin may bemixed and applied as one layer. Instead of anitrate layer, one mayemploy a layer of a mixed cellulose ester, such as hydrolyzed celluloseacetate propionate or butyrate. Asa matter of fact, any of the usualtypes of subbing layers which have been described in the prior art andwhich are compatible with the photographic emulsion layer to be employedand the melt-coating surface may be used if a subbing layer should bethought to be necessary. The sensitized emulsion which is employed maybe any of the usual gelatin silverhalide emulsions. 1n some cases it maybe desirable to employ an emulsion in which a cellulose ester isemployedas the protective colloid, such as described and claimedin U. S.. Patent2,110,491 of Salo. 1 1'The following-examples illustrate four inven..

ion: i 1 y Eamplclr-Porous waterleaf paper was ime pregnated by means ofhot calendering rolls. on a Waldron typemelt-coating machine after iirstheating the paper to 200--250v F. and coating it with a melt at 320 F.,consisting of 35% Aof cellulose acetate butyrate having a 50% butyrylcontent and 25 cps. Viscosity, 60% of chlorinated diphenyl having achlorine content of 65% vand 5% of dioctyl phthalate. Afterthusimpregnating the paper it was found to transmit a considerableamount of light or, in other words, exhibit a good degree oftranslucency. The translucent impregnated paper was then overcoated onthe melt-coating machine on both sides by heating the paper to 30G-330F. and then applying at a temperature of 350 F. a melt consisting'4 of.75 parts of cellulose acetate b-utyrate of 50% butyryl and 25 cps.viscosity, 15 parts of dibutyl sebacate, and l0 parts of butylstearate.The coating rolls were set so as to give a thickness on each: side ofapproximately .0005 inch, the melt having been applied at the rate ofsixpounds per 1.000 square feet of surface. The coated product which had alight transmission of about 60% was subbedby applying a thin layer ofcellulose nitrate oflow viscosity and then a thin layer of gelatinthereto; The paper was then coated with a photosensitiv gelatine-silverl,halide emulsion, land the result-q ing product was found to besatisfactory as a photographic copying and negatif e paper. Also, theproduct obtained was found to store satisfac- 'torily Example 2.-PorousWaterleai paper was im pregnated as described in the preceding enamplewith a mixture of 45 parte of low viscosity cellulose acetate butyratehaving a bu.J yl content of 50%, 50 parts of chlorinated diphenyl havinga chlorine content of 65% and 5 parte of dioctyl phthalate. Theimpregnated paper was then overcoated as described the preceding xample.The paper thus obtained was subbed and then coated with a photosensitivegelatin silver halide emulsion. A translucent photographic paper havinggoed properties was obtained.

Example 3.--Porous waterleaf paper was iinw pregnated as described inExample 1 with a corn-- position of 75 parts or" chlorinated diphenylhaving a chlorine content of 65% and 25 parts of cellulose acetatebutyrate having a butyryl content of 50% and a viscosity of 10centipoises. The impregnated paper obtained was then overcoated asdescribed in Example 1. A translucent photographic paper base wasobtained having good light transmission.

Example 4.-Porous Waterleaf paper was iinpregnated las described inExample 1 using a composition of 60 parts of polystyrene having a degreeof polymerization of about 60 and 35 parts of butyl stearato. Thethus-impregnated paper was overcoated with a melt composition asdescribed in the preceding examples. A translucent photographic paperbase having goed properties Was obtained.

When viscosities of cellulose acetate butyrates yare referred to in theabove examples, they are expressed in the viscosity of Aa solution ofone part of the ester in nine parts of acetone at 25 C. The lowviscosity butyric acid esters of cellulose which are employed in themelt-coating operation in preparing photographic paper in accordancewith our invention are those which have a melting point of less than 200C., a char point of at least 260 C., and preferably at least 300 C., afundamental cuprammonium viscosity of not more than centipoises, and anacetone viscosity Within the range of 5-100 centipoises. The celluloseester should have a butyryl content of at least 42% yand should behydrolyzed little, if any. For instance, a hydroxyl content of less than1 hydroxyl per 4 glucose units is typical of the hydroxyl content ofcellulose esters which are suitable. Some cellulose esters having the`properties stated and suitable for melt coating in accordance With ourinvention are:

1. Cellulose acetate butyrate, butyryl content 47.7%, acetyl content6.5%, acetone viscosity 24.9

i centipoises.

2. Cellulose acetate butyrate, butyryl content 49.4%, acetyl content5.6%, lacetone viscosity centipoises.

3. Cellulose acetate butyrate, butyryl content 48%, acetyl content 6.2%,acetone viscosity 15 Paper Impregnant Overcoating Wt. (lbs.) Wt. (lbs.)3 Wt. (lbs.) per Loco per Loco per 1,000 56%,;

sq. feet sq. feet sq. feet waterlca. l2 40 8. 9 3() 8. 8 30 D0 12 45 9.0 33 8 22 hemp paper. l 36 4. S 28 6. 1 36 The preparation oftranslucent paper base in accordance With our inve-ntion admits ofcontinuous operation in that paper sheet comes in the form of rolls, theusual melt coating machines are adapted for continuous operation, andthe temperatures used for impregnating the paper 4correspond fairlyclosely to those to which it is desirable to preheat the paper in themelt coating operation which constitutes the second step of our process.We have found that by preparing translucent paper base in this manner,the process become-s a unitary operation, the paper going in at one end,being coated with the impregnant, hot calendered, melt coated again toapply the overcoating thereto 'and coming out as a finished productwhich after having cooled below the melting point of the overcoating,may be collected on rolls.

W e claim:

l. A Water-prooi translucent paper consisting of paper having a looseporous structure impregnated with `a composition solid at roomtemperature consisting of cellulose 'acetate butyrate and chlorinateddiphenyl, the latter constituting at least 50% of the composition, whichcomposition has `a Viscosity of less than 5000 centipoises at C. and arefractive index approximately that of paper and having as an overcoatthereon a coating essentially consisting of cellulose lacetate butyrate,dibutyl seb'acate vand butyl stearate.

2. A water-proof translucent paper consisting of paper having a loose,porous structure impregnated with a composition solid at roomtemperature consisting of approximately 25 parts oi cellulose 'acetatebutyrate and approximately 75 parts chlorinated diphenyl whichcomposition. has a viscosity of less than 5000 centipoises at 170 C.anda refractive index approximately that of paper and having as anovercoat thereon a coating essentially consisting of cellulose acetatebutyrate dibutyl sebacate and ybutyl stearate.

MARTIN SALO. HAROLD F. VIVIAN.

References Cited in the file of this patent UNTED STATES PATENTS NumberName Date 2,108,805 Finzel et al. Feb. 22, 1938 2,410,685 Salo et al.Nov. 5, 1945 2,413,764 Hinman Jan. 7, 1947 2,415,631 Galley Feb. 11,1947 FOREIGN PATENTS Number Country Date 464,280 Great Britain 1937

2. A WATER-PROOF TRANSLUCENT PAPER CONSISTING OF PAPER HAVING A LOOSE,POROUS STRUCTURE IMPREGNATED WITH A COMPOSITION SOLID AT ROOMTEMPERATURE CONSISTING OF APPROXIMATELY 25 PARTS OF CELLULOSE ACETATEBUTYRATE AND APPROXIMATELY 75 PARTS CHLORINATED DIPHENYL WHICHCOMPOSITION HAS A VISCOSITY OF LESS THAN 5000 CENTIPOISES AT 170* C. ANDA REFRACTIVE INDEX APPROXIMATELY THAT OF PAPER AND HAVING AS AN OVERCOATTHEREON A COATING ESSENTIALLY CONSISTING OF CELLULOSE ACETATE BUTYRATEDIBUTYL SEBACATE AND BUTYL STEARATE.